Environmental Protection Agency (“EPA”) regulations require gasoline and diesel powered passenger cars and light trucks to incorporate on board hydrocarbon refueling emissions controls. As fuel is introduced into a motor vehicle's tank, the displaced vapors from the tank are directed to the refueling emissions controls. The goal is for the on board system to capture about 95 percent of the refueling emissions to limit the amount of volatile organic compounds (“VOCs”) and toxins emitted into the atmosphere during refueling. The VOCs that evaporate from gasoline during vehicle refueling contribute to urban ozone or smog formation.
Currently, vehicles use activated carbon-filled canisters to capture evaporative emissions. Carbon is “activated” by treating with steam or chemicals to increase porosity and generate a high surface area so that the activated carbon more readily adsorbs various chemical species. The activated carbon in the canister either is in the form of loose powders, granules or pellets, or in the form of a honeycomb extrusion, or a combination of these. The gas tank and fill pipe are designed so that when refueling the vehicle, fuel vapors in the tank travel to the activated carbon-packed canister where the vapors are adsorbed. Each filled canister weighs up to about 10 pounds. The carbon granules or pellets settle after being subjected to vehicle movement, which can change the flow path and alter filter performance. Carbon powders, granules or pellets generate dust, and the honeycomb extrusions lack significant vibrational stability, leading to breakage and dust generation. Lower cost, lighter weight, more resilient and more reliable alternatives to the activated carbon-packed canisters are sought.
One activated carbon canister system is shown in U.S. Pat. No. 6,540,815 (Hiltzik). In this patent, an emissions control system canister has a vent side that incorporates multiple beds of adsorbent materials that may be spaced apart by inert fillers or voidages, or has an adsorbent-containing monolith, such as a honeycomb, that has a desired void volume. When used, the inert fillers can be porous mats of foam. Such vent side absorbents are stated to have butane adsorption of about 6 g/dL. The '815 patent mentions activated carbon formed from various raw materials, including porous polymers, as a hydrocarbon adsorbent. In the working examples, the '815 patent uses foams only as inert or nonadsorbing material in combination with adsorbing activated carbon pellets. Such foams are not identified as hydrocarbon vapor adsorbents.
U.S. Pat. 6,464,761 (Bugli) discusses an air induction filter assembly that includes a reticulated multi-layer foam with carbon impregnation to remove residual hydrocarbon vapors diffusing through the inlet manifold of an engine after the engine is shut off. The '761 patent states that the carbon impregnated foam layer is optional in non-automotive applications where hydrocarbon adsorption is not required.
Foams have been used as fluid filtering media for different applications. SIF® foams from Foamex International Inc. of Linwood, Pa. are reticulated flexible polyester or polyether urethane foams with pore sizes from 10 to 110 pores per linear inch that may be used, for example, as gasoline fuel filters in chainsaws and other small engines. These foams filter particulates from liquids. PROTECTAIR® II foams, also from Foamex International, are reticulated polyether foams with pore sizes from 20 to 35 pores per linear inch that may be used, for example, in air filters to filter particulates from an air stream. Heretofore, such foams have not been used to adsorb hydrocarbons entrained in a gas stream.
In the 1980's, Scottfoam Corporation, a predecessor to Foamex International, offered an activated charcoal impregnated SIF® foam for use as a shoe sole insert under the trademark SORBACELL™. The Technical Data Sheet for this foam indicates that the foam was impregnated with high loadings (2 oz./square yard) of finely divided activated carbon particles, which allowed the coated foam to remove particulate material and adsorb some gaseous contaminants from an air stream.
Thus, the background art considered it necessary to treat or coat urethane or polymer filter material, such as foam, with activated carbon or other hydrocarbon adsorbent material in order to have a satisfactory butane working capacity and satisfactory hydrocarbon adsorption. Coated foams, however, can have higher weight, can be less resilient and can be more apt to generate particle contamination from flaking. Thus, it would be desirable to have a lower weight and more resilient filter material with satisfactory butane working capacity for use in evaporative hydrocarbon emissions systems.
In addition, automotive and engine-powered equipment manufacturers continue to seek systems and methods to reduce hydrocarbon emissions throughout the fuel and exhaust systems. To accomplish this, it would be desirable to have a low weight material to adsorb hydrocarbon gases that can be attached to or associated with regular and nonregular surfaces within a fuel and exhaust system.